Production Of Polyolefins By Metallocene Catalysts And Their Recycling By Pyrolysis

Polyolefins are the main industrial used polymers as they are sustainable materials. They show a wide variety of properties, consist of only carbon and hydrogen atoms, can efficiently be produced from easy available monomers and can be recycled. Beside Ziegler-Natta and Phillips catalysts, metallocenes and other transition metal complexes, activated by methylaluminoxane allow to tailor the structure, the tacticity, and the stereoregularity of polyolefins in a way which has not been reached before. Metallocene catalysts are able to copolymerize ethene or propene with different olefins, cyclic olefins, polar monomers as well as with macromers to form polymer short or long chain branched polymers with new properties. Polyolefin wastes can easily be recycled by extrusion moulding or by pyrolysis to gas and oil. While for extrusion moulding pure polymers have to be used the pyrolysis can take mixed and contaminated polyolefins. In a fluidized bed process, indirectly heated by fire tubes, different products are obtained in dependence of the pyrolysis temperature. By 500 degrees C about 90 % aliphatic waxes are formed, by 700 degrees C mainly olefins and aromatics. By addition of Lewis acids such as titanium or aluminum chlorides to the fluidized bed it is possible to decreasing the pyrolysis temperature by 100 degrees C.